1. Field of the Invention
The present invention relates to a pattern drawing apparatus which draws an exposure pattern for forming a concave/convex pattern for manufacturing information recording media, a method of manufacturing a master disk for manufacturing information recording media, using a concave/convex pattern formed using an exposure pattern drawn by the pattern drawing apparatus, and a method of manufacturing an information recording medium itself using the concave/convex pattern.
2. Description of the Related Art
Today, a demand for high density recording on magnetic recording and reproduction devices, such as HDDs, is more and more increasing. To increase the density of tracks by narrowing the tracks is now being studied as one of methods to fulfill the demand. In order to realize high density recording by this method, however, it is necessary to form a highly precise servo pattern which can realize accurate tracking servo, on magnetic recording media. In these days, it is popular to form a servo pattern by recording magnetically on each track via a magnetic head. In this case, as the density has become higher (the number of tracks has been increased), inaccuracy of the servo pattern, caused by inaccuracy in the positioning of the head, has come to be outstanding. Moreover, the time needed to record (form) the servo pattern has come to be longer. As a result, an increase in the manufacturing cost of magnetic recording and reproduction devices has been brought about. Some methods have been proposed in order to solve these problems. One of the methods is to magnetically transfer the whole of a servo pattern, formed with high accuracy beforehand, to the recording layer of a magnetic recording medium in a single operation, and another is to form the whole of physical asperities (protrusions and depressions) on a recording layer, as a servo pattern also formed with high accuracy, in a single operation.
More specifically, as the method of manufacturing an information carrier for transferring the whole of a servo pattern or the like to the recording layer of a magnetic recording medium in a single operation, there has been proposed a method of drawing an exposure pattern for forming a servo pattern or the like, using an electron beam exposure apparatus, in Japanese Laid-Open Patent Publication (Kokai) No. 2000-207738. In this method, as shown in FIG. 2 in the publication, firstly, a heavy metal film is formed on a ferromagnetic thin film formed on a non-magnetic substrate through vapor deposition of a heavy metal, such as Au, by the vacuum vapor deposition method. Secondly, after forming a resist film covering the heavy metal film, a predetermined pattern (mask) of a photoresist film is formed e.g. by the photolithography method. Next, a plurality of exposure position reference marks and a pattern center mark are formed on the ferromagnetic thin film, through etching of the heavy metal film e.g. by the dry etching method, using the formed pattern. Subsequently, an electron beam-sensitive resist is applied on the ferromagnetic thin film such that the resist covers the formed exposure position reference marks and the pattern center mark. Thus, a material on which a pattern is to be formed (material for drawing) is produced.
Then, as shown in FIG. 1 in the publication, the material for drawing is set on an electron beam drawing apparatus. At this time, the position of the pattern center mark on the material for drawing is detected by emitting an electron beam with an electron gun to detect reflected electrons with an electron detector, while driving an X-Y stage. Then, after rotating the material for drawing, through a predetermined angle by driving an air spindle motor, the position of the pattern center mark is detected again. As a result, an amount of deviation of the center of rotation of the material for drawing by the air spindle motor from the pattern center mark is calculated. Then, a pattern for manufacturing information carriers (information recording media) is drawn on the electron beam-sensitive resist, by the electron beam drawing apparatus. More specifically, the electron gun emits the electron beam to irradiate the electron beam-sensitive resist, while rotating the material for drawing by the air spindle motor. At this time, the emitted electron beam is reflected from exposure position reference marks. Therefore, by detecting reflected electrons using the electron detector, the moment in time at which the electron beam passes each exposure position reference mark (the irradiation position of the electron beam overlaps the exposure position reference mark) is detected.
Further, the electron beam drawing apparatus draws a portion of the pattern by performing ON-OFF control of the electron beam according to the shape of a pattern to be drawn, with reference to each time point the electron beam has passed an exposure position reference mark. In doing this, the irradiation position of the electron beam is finely tuned by an electron beam deflector, according to the amount of deviation of the center of rotation on the material for drawing from the pattern center mark. Further, after one rotation of the material for drawing, the material for drawing (air spindle motor) is moved radially by the diameter of a spot of the electron beam by driving the X-Y stage, and the drawing processing described above is continued. By executing the drawing process described above on the whole surface of the material for drawing, a pattern for manufacturing an information carrier is drawn on the electron beam-sensitive resists. After that, portions which are not irradiated with the electron beam are removed by processing the electron beam-sensitive resist to form a concave/convex pattern. Then, by etching the ferromagnetic thin film, using this concave/convex pattern as a mask, a thin film pattern is formed as shown in FIG. 3 in the publication, to complete a master information carrier.
From the study of the electron beam exposure apparatus described above, the present inventor found out the following points for improvement: In the conventional electron beam drawing apparatus, the moment in time at which the irradiation position of the electron beam overlaps an exposure position reference mark is detected by the electron detector. Then, the apparatus draws a desired pattern at a desired position of an electron beam-sensitive resist by performing ON-OFF control of the electron beam with reference to the moment of the detection. Therefore, it is necessary to form a plurality of exposure position reference marks in advance on the material on which a pattern is to be drawn. Because of this, the conventional electron beam drawing apparatus suffers from the problem that an increase in the manufacturing cost of master information carriers (information recording media) has been brought about, due to an extra process for forming a plurality of the exposure position reference marks on the material for drawing.